According to available information on the fracture toughness of high-strength alloys at low temperatures, the effect of low temperatures on toughness is generally dependent on the alloy base. For many aluminum alloys, the fracture toughness tends to increase or remain generally constant as the testing temperature is decreased. Titanium alloys tend to have lower toughness as the testing temperature is decreased, but the effect is influenced by the alloy content and heat treatment. Certain titanium alloys retain good toughness at very low temperatures. Alloy steels normally exhibit decreasing fracture toughness as the testing temperature is decreased through the transition temperature range, when the structure contains ferrite or tempered martensite. The transition temperature is influenced by the alloy content, grain size, and heat treatment. Low temperatures apparently have little effect on the fracture toughness of Inconel Alloy 718. These trends are reviewed based on current state-of-the-art information. Limited information on the fatigue crack growth rates of 2219-T87 aluminum alloy and Ti-6A1-4V alloy indicate that the slope of the da/dN curves is changed as the testing temperature is decreased.